This invention relates to a device for detecting acceleration, and more particularly, relates to an acceleration detector which uses a strain gauge.
A conventional acceleration detector uses a strain gauge. As shown in FIG. 4, the conventional acceleration detector has a beam 91, an arm 92 fixed to the beam 91 and a weight 93 held at one end of the arm 92. Each end of the beam 91 is supported on a support 961. The base of the arm 92 is fixed by rivets 94 to a middle part in the lengthwise direction of the beam 91. A strain gauge (not shown) is provided on the beam 91.
The arm 92 is made of an elastic material. A holder 921 is formed by bending a middle portion of the elastic material and is located at a left end portion of the arm 92. At the holder 921, the weight 93 is held. A weight stopper 95 is fixed on the support 961. The weight stopper 95 regulates a stroke of the weight 93 when over shock is added thereto.
The stroke regulation of the weight 93 is important for the acceleration detector. If the beam 91 receives a force over a surrender point of the beam 91 or the strain gauge, plastic deformation of the beam 91 or a break of the strain gauge pattern may occur resulting in the change of the character of the acceleration detector. So, the stopper 95 prevents the above problem.
It is to be noted that in FIG. 4, reference numerals "97" and "98" indicate a cover and terminals for getting an output from the strain gauge, respectively.
In the above conventional acceleration detector, the arm 92 is made of the elastic material and the weight 93 is held at the end of the arm 92. Thus, the center of gravity of the weight 93 is subject to shift in the detecting direction corresponding to the vertical direction in FIG. 4 due to the accuracy in the working of the arm 92. When the center of gravity shifts, a clearance S1 between the holder 921 and the stopper 95, and a clearance S2 between the holder 921 and a bottom surface 962 of the base 96 are changed severely.
Further, the weight 93 is formed to a rectangular shape. Thus the clearances S1 and S2 are defined by the upper surface or bottom surface of the holder 921, and touching points between the stopper 95 or the base 96 and the holder 921 are unstable upon receipt of over shock. The touching points are shifted by a twist of the beam 91 so that the clearances S1 and S2 are changed. Thus it is difficult to obtain a satisfactory clearance accuracy for each clearance, which causes a poor shock-proof device.
Further, in the conventional acceleration detector, the arm 92 is made of metal so that the weight of the arm 92 is heavy. Thus it is difficult to concentrate the center of gravity of the weight 93 at the top end of the arm 92 so that the sensitivity of the detector is poor.
Furthermore, in the conventional acceleration detector, the rectangular shape of the weight 93 increases the moment of inertia upon distortion of the beam 91. It is difficult to get high accuracy from the detector.